Abstract

The authors have investigated the magnetic properties of a digital ferromagneticheterostructure (DFH) showing ferromagnetic behavior using soft x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). The Mn -edge XASspectra were similar to those of random alloy thin films, indicating a substitutional doping of high concentration Mn into GaN. From the XMCD measurements, it was revealed that paramagnetic and ferromagnetic Mn atoms coexisted in the digital layers. Subtle differences were also found from the XMCD spectra between the electronic states of the ferromagnetic and paramagnetic ions. The ferromagnetic moment per Mn atom estimated from XMCD agreed well with that estimated from superconducting quantum interference device measurements, indicating that the ferromagnetic behavior of the DFH sample arises only from substitutional ions in the digital layers and not from ferromagnetic precipitates.

Received 24 March 2007Accepted 18 July 2007Published online 15 August 2007

Acknowledgments:

This work was supported by a Grant-in-Aid for Scientific Research in Priority Area “Semiconductor Nano-Spintronics” (14076209). The authors also thank the Material Design and Characterization Laboratory, Institute for Solid State Physics, University of Tokyo, for the use of the SQUID magnetometer.